dm: use signal_pending_state() in dm_wait_for_completion()

Use signal_pending_state() instead of open-coding it.  This patch does
not change any functionality but makes it possible to pass TASK_KILLABLE
as the second argument of dm_wait_for_completion().  See also commit
16882c1e962b ("sched: fix TASK_WAKEKILL vs SIGKILL race").

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm.c

@@ -1954,8 +1954,7 @@ static int dm_wait_for_completion(struct mapped_device *md, long task_state)
 		if (!md_in_flight(md))
 			break;
 
-		if (task_state == TASK_INTERRUPTIBLE &&
-		    signal_pending(current)) {
+		if (signal_pending_state(task_state, current)) {
 			r = -EINTR;
 			break;
 		}